Radio receiver control means



June 26, 1945. R. P l MER I 2,379,284

RADIO RECEIVER CONTROL MEANS Filed Oct. 11, 1943 4 Sheets-Sheet 1 FIG. I

INVENTOR. nun ROBERT F! DIMMER "I". BY IllllllllllllllllIlllllliilH ATTORNEYS June 26, 1 945.

R. P. D IMMER RADIO RECEIVERCONTROL MEANS Filed Oct. -11, 1943 4 Sheets Shet :s'

W mmyron ROBERT P. DIMMER ATTORNEY-S June 26, 1945. R. P. DIMMER RADIQ RECEIVER CONTROL MEANS Filed Oct. 11, 1945 4 Sheets-Sheet 4 IN VEN TOR.

ROBERT P DIMMER ATTORNEYS Patented June 26, 1945 RADIO RECEIVER CONTROL MEANS Robert P. Dimmer, Chicago, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware 1 Application October 11, 1943, Serial No. 505,771

8 Claims.

The present invention relates to radio receivers and, more particularly, to a unitary control means for changing the frequency range of the radio receiver and for changing the frequency of the intermediate frequency amplifier.

It has been common in multi-band radio receivers to provide a band switching arrangement for changing the frequency range over which the receiver is to be operative. Heretofore such arrangements have generally operated to connect into circuit a selected one of a plurality of tuning inductors in the radio frequency input and the radio frequency amplifier portion of a receiver by merely completing the necessary connection. In a radio receiver which has a high overall gain, as, for example, a receiver utilizing a rather small loop antenna, the ordinary band switching schemes are inadequate. Furthermore, where a radio receiver is to operate over a wide range of frequencies, as, for example, one band might be 2 to 3 megacycles and a band at the other range of frequencies might be from 30 to 50 megacycles, in order that the tuning inductors be provided to cover these frequency ranges and other intermediate frequency bands, it is necessary to enclose each tuning inductor in a separate shielded container and, furthermore, to short circuit each unused tuning inductor so that it will'be unable to affect the operation of the receiver. The.

intermediate frequency amplifier also must be arranged to operate at one frequency for the lower radio frequency band operation and at another frequency for the higher radio frequency band operation.

In accordance with the present invention a unitary control means is provided for selectively changing the frequnecy range of the radio receiver and for changing the frequency range of the intermediate frequency amplifier. This unitary control means for the radio frequency amplifier and the intermediate frequency amplifier comprises a single actuating member arranged to be moved to any one of a plurality of predetermined positions, each of which corresponds to a particular band over which the radio receiver is to operate, and in accordance with a shift from the lower radio frequencies to the higher radio frequencies the same apparatus operates to change the operating frequency of the intermediate frequency amplifier. In order to provide for the simultaneous switching into operation of a plurality of radio frequency tuning inductances it has been found advantageous to cause a single cam to actuate all of the switches associated with a particular frequency band. In order that these various switches might be operated simultaneously, adjustable operating means are provided which interconnect the various switchactuating means of the radio frequency tuning inductances.

Therefore it is an object of the present inven-- tion to provide in a radio receiver an improved unitary control means for selectively changing the frequency range of the radio receiver and for changing the operating frequency of the intermediate frequency amplifier.

Another object of the present invention is to provide in a radio receiver an improved unitary control means for selectively changing the frequency range of the radio receiver and which is provided with adjustable means whereby simultaneous switching of a plurality of switches-associated with a plurality of radio frequency tuning inductors may be obtained.

The invention itself is set forth with particularity in the appended claims. Other and further objects of the present invention will subsequently become apparent by reference to the following description taken in connection with the accompanying drawings, wherein Figure 1 is a top View of a portion of a radio receiver chassis provided with the present invention; Fig. 2 is a view partly in cross section along the line 22 of Fig. 1; Fig. 3 is a detailed view of the switch contacts shown in a part of Fig. 2; Fig. 4 is a top view of the switch contacts shown in Fig. 3; Fig. 5 is a side view of the switch contacts contained within the intermediate frequency transformer shield; Fig. 6 is a top view of the switch contacts shown in Fig. 5; and Fig. '7 is an end view of a portion of certain apparatus shown in Fig. 1; and Figs. 8, 9 and 10 show a circuit utilizing the apparatus comprising the present invention.

Referring more particularly to Figs. 1 and 2, there is shown a radio chassis ii having a front supporting panel l2 and a side wall 23. Mounted on the chassis ll are a plurality of containers l4 and 15 each comprising a shield containing a radio frequency tuning inductor and a switch. While only two radio frequency units it and it for a two stage radio frequency amplifier have been shown, it, of course, will be appreciated that a greater number might be utilized, wherefore the additional units would correspond more nearly to the radio frequency unit M. It, furthermore, is to be understood that while only one group of such units is visible in the drawing by virtue of the break in the chassis, other grou s of such units are provided, each group corresponding to the apparatus associated with the various stages of radio frequency amplification in a selected band of frequencies. It furthermore will be appreciated that where each stage of amplification is to be arrangedto operate over a plurality of frequency bands, all of the inductors for a single stage might be contained within a single shielded structure which, of course, would then be provided with a plurality of switches corresponding to the number of inductors contained therein. Th various shielded structures, however, would be aligned along the axes of the switch actuating means and in order that the switches operate simultaneously, adjustable means are provided so that the entire series of switches will operate at the same time. The switching apparatus provided for the control of the radio frequency transformers or inductors and also for the intermediate frequency transformers comprises a shaft l6 suitably supported upon the radio receiver chassis I and extending to the exterior of the front panel l2 where the shaft is provided with a suitable actuating knob H. The shaft I6 is arranged to be angularly displaced to a selected one of a number of predetermined angular positions. In order to retain the shaft I6 in any selected predetermined position there is provided a suitable retaining mechanism H! which is also shown in Fig. 7 and which will subsequently be described in detail. Beyond the retaining apparatus l8 the shaft i6 is provided with a plurality of adjustably positioned cams, such as cams l9, 2|, 22 and 23. The latter cams 2| to 23 are arranged to control the operation of a plurality of intermediate frequency transformers contained within suitable shielded housings 24 and 25.

The cam I9 is arranged to control the radio frequency tuning inductors contained within the shielded containers I4 and I by a cam follower apparatus engaging the surface of the cam I9. This cam follower apparatus includes a rod 26 suitably supported in bearing members 21 and 28 p sitioned in the sides of the shielded container structure |4. At an intermediate point on the cam follower rod 26 there is suitably secured a switch actuating block 29 which is provided with a conical aperture into which there is fitted the movable switch blade 3| which cooperates With relatively stationary switch blades 32 and 33 positioned at opposite sides of the switch blade 3|. The lower extremities of all the switch blades 3| to 33 are secured in suitably insulated supporting means 34.

In the position shown in Fig, 2 the cam I! has actuated the switch blade 3| from the off-normal position so as to remove the short circuit from the associated tuning inductor connected across the switch blades 3| and 32 and to connect into circuit the associated tuning inductor by contact with the switch blade 33. One extremity of the rod 26 is arranged to bear against the movable member, such as the cam surface l9, and the other extremity of the rod 26 is provided with a tapped opening 39 into which there is fitted a threaded screw member 4|. The position of the threaded screw member 4| may be varied and secured in a desired position by the application of a lock nut 42 bearing against a suitable washer 43 which engages the end of the shaft member 26. The adjustable spacing means comprising the threaded screw member 4| and lock nut 42 permlts compensation for slight displacements in the assembly of the individual shielded units relative to each other. Thus there is provided an arrangement which is readily installed and which, nevertheless, will provide for simultaneous operation of all of the switches involved at any one selected time. The head of the screw 4| is arranged to engage one end of another movable shaft, such as 26 or 44, where the succeeding radio frequency tuning inductor is housed in a struc ture similar to the one just described. In other words, a number of units such as M may be provided in seriatim which is terminated by a unit such as l5 which is provided with a longitudinally movable shaft member 44 which also actuates a switch structure corresponding to that shown in the cross-sectional View of the shielded container M. The other end of the movable shaft member 44 is engaged by a flat spring member 45, one end of which is secured to one side of the shield IS. The flat spring member 45 urges all of the rods, such as 44 and 25, toward the cam I9 so that the high portion of the cam I9 will simultaneously actuate all of the switches contained within the shielded containers, such as l4 and 15.

The switch structure utilized within the shielded containers l4 and I5 is one which provides positive contact operation with a minimum amount of movement and which has its switch blades so formed that the inter-element capacity is reduced to a minimum. By referring to Figs. 3 and 4 it will be seen that the lower extremity of each of the switch blades 3| to 33 is in the form of a rod or wire, as contrasted to the usual flat spring structure which has a much greater interelement capacity. The upper extremity of each of the switch blades 32 and 33 is provided with arcuato shaped contact portions 20 and 30, respectively, which are arranged to be engaged by an intermediate portion of the center switch blade 3|.

Reference may now be had to Figs. 1, 5 and 6, from which it will be seen that each intermediate frequency transformer container, such as 24, is associated with two operating cam menn bers such as 2| and 22. Suitable bearing members 46 and 41 are each secured in position by cooperating lock nuts 48 and 49. Each of the members 46 and 41 is provided at its interior portion with an enlargement such as the enlargements 5| and 52 which bear against the inside of the shielded structure 24. These bearing members are provided with a cylindrical opening within which there is supported a member having rod-like outer terminations 53 and 54, respectively, having inner terminating portions 55 and 55 which are more or less rectangular in cross section. The rectangular end portion 55 is provided with a pair of notches which engage movable spring contacts 51 and 58 arranged to co operate with the relatively stationary contacts 5|! and 6|. Similarly, the end portion 56 of the other switch actuating apparatus is provided with notches engaging movable contacts 62 and 63 ar ranged for cooperation with the relatively stationary contacts 64 and 65. One of the corn tacts 51 is visible in Fig. 5 and this contact co operates with the contact 59. The contact 51 is also arranged to cooperate with another relatively stationary contact 65 with which it is in engagement whenever the actuating portion 53 is not in engagement with the high portion of a cam, such as the cam 22. Another similar contact is arranged for cooperation with the contact 58 so that the two movable contacts 51 and 58 actuated by the rod 53 are arranged to switch the conductors leading to the associated vacuum tubes from one intermediate frequency transformer to another intermediate frequency transformer.

For certain conditions of operation of the radio-receiver it is desired to broaden the response of the intermediate frequency transformer and in order to efiect this the cam 2I was provided to actuate the rodlike member 54. Each of the pairs of contacts 62, 64 and 63, 65 is arranged to connect across one winding of the associated intermediate frequency transformer a broadening resistor. It will be noted that the switch blades, such as 51, 59 and 66 shown in Fig. 5, are of a configuration and structure analogous to the type of switch blades shown in Figs. 3 and 4. In other words, the movable switch contact 51 is a cylindrical rod or wire which cooperates with cylindrical or wirelike switch contact members 59 and 66, the free extremities of which are provided witharcuate end portions for cooperation with a movable switch contact.

In order that the shaft I may be retained in any one of a plurality of predtermined positions, there is provided the retaining means I8 which is also shown in Fig. '7. Mounted upon the shaft I6 is a detent wheel 61 having a plurality of semicircular notches arranged about its periphery. These notches are engageable with a roller 60 supportedat an intermediate point on a channel-like lever 69. The channel-like lever 69 is pivoted at one end and supported by a suitable bracket II secured to the chassis II. Adjacent the roller 68 the lever 69 is provided with a pair of projecting ears 12 extending on either side of the detent wheel 61. Extending beyond the roller 68 is an angular portion I0 provided with a notch which is engaged by a biasing spring 13. The otherextremity of the biasing spring I3 engages a bracket I4 secured to the side wall I3 of the chassis. This arrangement utilizing a U-shaped channel structure for the lever 03 which has cooperating cars 12 at either side of the detent wheel 61 insures positive cooperation of the roller 68 with the notches in the detent wheel. Such structure, furthermore, by having the roller 60 at an intermediate point on the lever 69, has the advantage of providing a positively engaging detent which is relatively free from vibration whenever the roller 68 engages one of the detent Wheel notches as the shaft I6 is rotated. This produces a positive centering action so that the cams associated with the shaft I6 are properly stopped at the correct angular displacement. The circular notch and roller arrangement furthermore permits rapid adjustment to other positions and, as each new position is encountered, this is distinctly felt by the operator ofthe knob H.

In order to illustrate more-clearly the manner in which the apparatus shown in Figs. 1 to 7 cooperates to produce the desired changes in the operation of a radio receiver, a portion of such receiver has been shown in Figs. 8, 9 and 10. It may be assumed that the receiver is to operate over a number of bands such as 2 to 3 megacycles, 3 to 4.5 megacycles, to megacycles, and 30 to megacycles. Because of the diiference between the lower frequency bands and the higher frequency bands it is desirable to provide for the operation of the intermediate frequency amplifier at two difierent frequencies. The radio receiver is arranged to be energized from a suitable antenna which has been illustrated in. Fig. 8 as comprising a loop antenna IOI connected to the movable contact arms I02 and I03 of a pair of switches each having a plurality of contacts.

I02and I03 are connected to the upper and lower terminals of the primary windings of a plurality of radio frequency input transformers The contacts of the switches I04, I05, I00 and I01. Each of the transformers I04 to I0! is provided with an electrostatic shield between the primary and secondary windings so that the antenna IN is maintained balanced with respect to ground.

The secondary windings of the transformers I04 to I01 are each connected to one of a plurality of single pole double throw switches I08, I09, I I0 and I I I which are arranged so as to normally short circuit the secondary windings so that any transformers not in use will not affect the operation of the radio receiver. One of the contacts of each of the switches I08 to II I is connected to the control grid or electrode of a vacuum tube II2 which is also connected to one section I I3 of a single control variable capacitor. In order to obtain the optimum resonant condition-of the input circuit of the vacuum tube I I2 an auxiliary or Vernier capacitor I I4 may be connected to capacitor II3. Both the capacitors are connected to ground. The cathode of the vacuum tube I I2 is suitably biased by self-biasing resistors I I5 and H6, the latter one being adjustable so that the gain of the radio frequency amplifier might be controlled manually. The cathode of the vacuum tube H2 is by-passed to ground by the capacitor I20. The anode circuit. of the vacuum tube includes a radio frequency choke coil II'I connected to a resistor I I8 which, in turn,is connected to a suitable source of anode potentials The resistor H8 is by-passed to ground by a capacitor H9. The screen grid of the vacuum tube II2 receives potential through a voltage drop resistor I2I connected to the common juncture between the choke coil II'I and the resistor H8. The resistor and the screen grid are by-passed to ground by a capacitor I22. The anode of the vacuum tube H2 is capacitively coupled bythe coupling capacitor I23 which is connected to the control electrode of the succeeding vacuum tube 20I.

The input circuit to the vacuum tube 20I is tuned by another section 202 of the same gang capacitor which tunes the input to the preceding amplifier tube. A plurality of tuned inductors or impedances are arranged for selective connection to the input of the vacuum tube 20I by a plurality of single pole double throw switches 203 to 206 each arranged to normally short circuit its associated tuned circuit. The switch 203 is connected to a circuit including an inductor 201 and The switch 204 is assoa trimmer capacitor 208. ciated with an inductor 209 and a trimmer capacitor 2II. inductor 2I2, a trimmer capacitor 2 I3 and a broadening resistor 2I4. The switch 206 is associated with an inductor 2I5, a trimmer capacitor 2I6 and a broadening resistor 2". The cathode of the vacuum tube 20I is by-passed to ground by a capacitor H8 and is biased by the resistors 2I9 and H6.

In a manner similar to the preceding stage of amplification the anode of the vacuum tube 20I is connected to a radio frequency choke coil 22I, a resistor 222 and a grounded capacitor 223. The screen grid is by-passed to ground by a, capacitor 224 and receives its supply of potential through a voltage drop resistor 225, which is connected to the ncture between the choke coil 22I and the resistor 222. The anode of the vacuum tube MI is coupled through a capacitor 226 to the input electrode of the succeeding vacuum tube 30I which serves as the first detector of the radio receiver set. The input circuit of the vacuum tube 30I is arranged to be tuned by another section The switch 205 is associated with an 221 of the same gang capacitor which tunes the preceding stages.

The grid circuit of the vacuum tube 30| is associated with a plurality of switches 228, 229, 23| and 232 which are selectively operable to connect into circuit tuned circuits comprisin inductors and capacitors, and in certain cases broadening resistors in a manner similar to the input circuit of the vacuum tube L In addition the vacuum tube 30l is provided with an oscillator section connecting the cathode and one of the grids. This grid is provided with a grid resistor 238 which is grounded and a blocking capacitor 234; The capacitor 234 is connected to a plurality oi single pole single throw switches 235 to 238. The cathode of the vacuum tube 30| is connected to one contact of a plurality of single polo double throw switches 2 to 244, which are arranged so as to normally short circuit one half of an associated inductor such as the inductors 245 to 248, respectively. Inductors 245 to 248, respectively, are associated with trimmer capacitors 249, 250, and 252. Interposed between the switches 238 and 231 is a padding capacitor 239. Interpo'sed between the switch 231 and the inductor 241 is a padding capacitor 253, and similarly between the switch 238 and the inductor 248 is 9. padding capacitor 254. The padding capacitors and the trimmer capacitors cooperate with a variable capacitor 255 which comprises another section of the gang control capacitors.

In order to illustrate how a cam, such as I9, simultaneously operates a plurality of switches to change the band over which the radio frequency amplifier operates, a dotted line has been drawn between the switches I02, I03, I08, 203, 228, 235 and 24| to show that these switches will be operated by a single cam. The inductors or transformers associated with such switches are contained within a series of shielded structures such as H and I5 shown in Fig. 1. Another cam similar to cam |9 would be utilized to control switches I09, 204, 229, 236 and 242, and still another cam would control the switches H0, 205, I, 231 and 243, etc.

The vacuum tube 3! is provided with a grounded suppressor grid, and with screen grids which are energized from a suitable source of potential through the voltage drop of resistors 302 and 303. The connection to the grids and the resistor 303 is by-passed to ground by a capacitor 304. If desired a voltage regulator tube 305 may be connected between ground and the common juncture of the resistors 302 and 303.

The intermediate frequency amplifier may comprise a plurality of stages of amplification and for the purposes of illustration two such stages have been shown in Fig. 10. The intermediate frequency amplifier normally operates at a certain frequency as determined, for example, by the operation of transformers 308 and 301. When it is desired to operate the intermediate frequency amplifier at another frequency alternate transformers 308 and 309 are switched into the circuit. A pair of switches 3H and 3|2 control the connections to the transformers 306 and 308. The transformer 308 is normally con nected by the switch 3|| to the anode of the vacuum tube L The primary winding of the transformer 306 is provided with a trimmer capacitor 3|3 which operates in parallel with a padding capacitor 3|4. Suitable anode potential is provided through a voltage drop resistor 3l5, one terminal of which is by-passed to ground by a capacitor 3|0. The resistor 3l5 is connected between ground and the control electrode of the succeeding vacuum tube 3|9. Thus normally the switches 3H and 3|2 connect the transformer 308 between the vacuum tubes MI and 3|0. When the switches 3H and M2 are actuated they are arranged to connect the transformer 308 between the vacuum tubes 30| and Ill.

The primary winding of the transformer 300 is tuned by a trimmer capacitor 32| arranged to operate in parallel with the padding capacitor 3. The secondary winding of the transformer 308 is tuned by a trimmer capacitor 322 arranged to operate in parallel with the padding capacitor 3 I 8. The cathode of the vacuum tube 3 I 9 is connected through a resistor 323 to a suitable source of gain control bias. The cathode of the vacuum tube 3|9 i by-passed to ground by a capacitor 324.

The transformers 301 and 309 are arranged to couple the vacuum tube 3|9 to a succeeding amplifying tube or second detector. A pair of switches 326 and 321 normally connect the transformer 301 between the vacuum tube 3|9 and the next vacuum tube. The primary winding of the transformer 301 is tuned by a trimmer capacitor 328 arranged to operate in parallel with a padding capacitor 329. The secondary winding of the transformer 301 is tuned by a trimmer capacitor 33| arranged to operate in parallel with a padding capacitor 332.. The primary winding of the transformer 309 is provided with a trimmer capacitor 333 arranged for operation in parallel with the padding capacitor 329. The secondary winding of the transformer 309 is provided with a trimmer capacitor 334 arranged for operation in parallel with the padding capacitor 332, Suitable anode voltage is supplied to the vacuum tube 3|9 through a voltage drop resistor 335 which is connected to a grounded by-pass capacitor 336 and to one terminal of the primary winding of the transformers 301 and 309. From this common connection to the primary windings of the transformers 301 and 309 there is provided a voltage drop resistor 331 connected to the screen grid of the vacuum tube 3|9. The screen grid is by-passed to ground through a c8- pacitor 338.

It thus becomes apparent that with the connections as shown, the vacuum tubes 30| and 3|9 and the succeeding vacuum tube are interconnected normally by transformers 306 and 301. In order to change the frequency of the intermediate frequency amplifier a pair of cams, such as the cams 2| and 23, are arranged to actuate simultaneously the switches 3H, 3|2, 328 and 321. In addition two other cams corresponding to cam 22 are provided for broadening the frequency response characteristic of the intermediate frequency transformers. These cams are arranged to actuate pairs of switches, such as the pair of switches 339 and 340 associated with the transformers 30B and 308. A pair of resistors 34| and 342 are associated with the switches 339 and 340 so that when these switches are actuated the resistors are effectively connected across the primary and secondary windings of the transformer then interconnecting the vacuum tubes 30| and 3|9, dependent upon the condition of operation of the switches 3H and 3|2. Similarly a pair or switches 343 and 344 are provided for cooperation with a pair of resistors 345 and 346 arranged to be connected across the windings of either of the transformers 301 Or 309, depenent upon whether or not the switches 326 and 321 have been actuated. Thus a single pair of resistors is provided for each set of intermediate frequency transformers for controlling the response characteristic thereof. Thus these resistor controlling switches are actuated by a cam corresponding to the cam 22.

While one embodiment of the invention has been disclosed, it will be understood that various modifications may be made therein which are within the true spirit and scope of the invention.

What is claimed is:

1. In a radio receiver, the combination comprising a radio frequency amplifier having a plurality of tuned circuits for each stage, an electricswitch for each circuit including contacts for short-circuiting each of said tuned circuits, an intermediate frequency amplifier having an electric switch and two sets of tuned circuits for each stage, and a single control means for selectively changing the frequency band of said first amplifier and for changing the frequency of said intermediate frequency amplifier comprising a rotatable shaft provided with means for retaining said shaft in any selected one of a plurality of predetermined positions, said shaft being provided with a plurality of angularly adjustable cams, certain of said cams each being arranged to control the switches and said short-circuiting contacts of said turned circuits of said radio frequency amplifier, thereby to connect the tuned circuits of a particular frequency band to said radio frequency amplifier and to remove the short circuit from the connected ones of said tuned circuits, certain other of said cams being arranged to control the switches of said tuned circuits of said intermediate frequency amplifier, and means for indicating the position of said shaft.

2. In a radio receiver having a plurality of vacuum tubes the combination comprising a plurality of radio frequency transformer units each having a shielded housing containing a tuning inductor, a switch and longitudinally reciprocable means for actuating said switch,

said plurality of transformers being adapted to be connected in operative relation with said plurality of vacuum tubes whereby said radio receiver will operate over a selected frequency band, said transformer units being aligned along the axis of said longitudinally reciprocable actuating means, a single control means arranged to move said longitudinally reciprocable actuating means, and means for biasing all of said actuating means toward said control means.

3. In a radio frequency amplifier adapted to operate over one of a plurality of selected frequency bands, the combination comprising a plurality of radio frequency inductance units each comprising a shielded housing containing a tuning inductor, a switch therefor and a longitudinally reciprocable switch operating rod, said radio frequency units being arranged with the switch operating rods in axial alignment, a cam for actuating said operating rods, means associated with the end one of said units for urging said rods towards said cam, each of the other of said units being provided with adjustable means mounted on one end of its operating rod whereby the switches of said rods may be caused to be operated simultaneously by said cam. f

4. In a radio frequency amplifier adapted to operate at any one of a plurality of selected frequency bands, the combination comprising a plurality of radio frequency tuning units each comprising a shielded housing containing a tuning inductor, a switch therefor and a longitudinally operating rod, said radio frequency units being arranged with switch operating rods in axial alignment, a cam for actuating said operating rods, means associated with the end one of said units for urging said rods towards said cam, and means mounted on said rods intermediate said radio frequency tuning units for aligning the operating positions of said rods to obtain simultaneous operation of the switches controlled by said rods.

5. In a radio frequency amplifier adapted to operate at any one of a plurality of selected frequency bands, the combination comprising a plurality of radio frequency tuning units each comprising a shielded housing containing a tuning inductor, a switch therefor and a longitudi nally reciprocable switch operating rod, the rods of each of said radio frequency units except one being provided adjacent one end with a longitudinally adjustable spacing means, said one radio frequency unit being provided with biasing means urging its rod in one direction, a cam for actuating said rods, said radio frequency units being positioned in seriatim with the operating rods in axial alignment and with said one radio frequency unit positioned farthest from said cam whereby all said rods are biased towards said cam.

6. In a radio frequncy amplifier adapted to operate at any one of a plurality of selected frequency bands, the combination comprising a plurality of groups of radio frequency tuning units, each group being operative to cause said radio frequency amplifier to operate over a different frequency band, each group of tuning units comprising a plurality of shielded housings each containing a a, tuning inductor, a switch and a longitudinally reciprocable switch actuating means, said tuning units of said group being aligned along the axis of said actuating means, a rotatable cam arranged for cooperation with said actuating means, and means associated with the remote shielded housing for urging all of said switch actuating means towards said earn.

7. In an intermediate frequency amplifier adapted to operate at either of two frequencies, the combination comprising a pair of intermediate frequency transformers for each stage of said amplifier, a pair of transformers enclosed within a shielded housing, a plurality of switches supported by said housing, a pair of resistors supported within said housing, certain of said switches being arranged to selectively connect said transformers in and out of circuit with an associated stage of said amplifier, certain of said other switches being arranged for selectively connecting said resistors across the windings of either of said transformers thereby to broaden the response characteristic thereof, a single control means for actuating said switches comprising a shaft having a predetermined angular positions, a pair of cams supported on said shaft for each of said shielded housings, and means interconnecting said switches with said cams.

8. In a radio receiving set capable of being tuned to a number of different frequency bands, the combination of a radio frequency amplifier having a high frequency tuning system comprisfor actuating said cams to select a particular one of said groups of tuning units at a time, thereby to actuate said operating elements of the tuning units of a predetermined frequency band to connect the selected group of tuning units to said amplifier and to actuate the associated contacts to remove the short circuit from the selected tuning units.

ROBERT P. DIIWIVIER.

. CERTIFICATE OF CORRECTION. Patent No. 2,579,28L I June 26, 19L

ROBERT P. DIMIIER.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line 55 claim 1, for the word "turned" read --tuned--; and second column, line 67 claim 7, before "predetermined" strike out "a"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office Signed and sealed this 9th day of October, A. D. 194.5.

Leslie Frazer (Seal) First Assistant Commissioner of Patents CERTIFICATE OF CORRECTION.

Patent No. 2,579,28li. June 26, 1914.5.

ROBERT P. DINNER.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first Column, line 55, claim 1, for the word "turned" read -tuned-; and second column, line 67, claim 7, before "predetermined" strike out "a"; and that the said Letters Patent should be read with this correction therein that 'the same may conform to the record of the case in the Patent Office.

Signed and sealed this 9th day of October, A. D. 1914.5.

Leslie Frazer (Seal) First Assistant Commissioner of Patents 

